1. Field of the Invention
The invention relates to an in-cylinder air amount estimation apparatus for an internal combustion engine, and an estimation method thereof.
2. Description of the Related Art
In an internal combustion engine, operation control such as fuel injection amount control is performed based on an amount of air in a cylinder when an intake valve is in a closed state (hereinafter, referred to as “in-cylinder air amount”). Therefore, it is important to accurately estimate the in-cylinder air amount in order to appropriately perform the operation control.
Accordingly, for example, Japanese Patent Laid-Open Publication No. 2001-234798 discloses a technology in which intake efficiency in each cylinder is estimated, and the intake efficiency is used to estimate an in-cylinder air amount in a corresponding cylinder. In this case, even if the intake efficiency varies with each cylinder due to, for example, adherence of deposits in an intake system of an internal combustion engine, or deviation of components caused when assembled, and therefore the in-cylinder air amount varies with each cylinder, the in-cylinder air amount can be estimated considering the variation.
Meanwhile, in the internal combustion engine, intake valves of the cylinders are sequentially opened, which causes pulsation of a pressure in an intake pipe. This pulsation of the pressure in the intake pipe is closely related to the in-cylinder air amount in each cylinder. However, in the technology disclosed in the Japanese Patent Laid-Open Publication No. 2001-234798, the aforementioned pulsation is not considered when the in-cylinder air amount in each cylinder is estimated. Therefore, the estimated in-cylinder air amount in each cylinder becomes inaccurate due to influence of the aforementioned pulsation.